Immunogenic assays involving an antibody antigen reaction to detect an antibody or antigen in biological samples have been an important tool in the in vitro diagnosis of human diseases or disorders. In carrying out such immunogenic assay, microtiter plates or trays have become an important tool particularly in the detection of Human Leucocyte Antigen (HLA) as well as certain genetic information which may be present on the surface of nucleated cells, such as lymphocytes. This information is extremely useful in organ transplantation and parentage testing. Tissue typing assays have been standardized to promote accuracy as well as reproducibility of results. Part of this accepted standardization of the assay involves use of the "Terasaki" style microtiter tray set forth in U.S. Pat. No. 4,599,315, issued Jul. 8, 1986. This is a small plastic tray (approximately 5 cm.times.7 cm) containing a number of reaction wells. Other types of microtiter trays or plates are disclosed in U.S. Pat. No. 4,735,778.
The standard plastic microtiter tray is made of a light transmitting hydrophobic polymer such as polystyrene. It is important that the plate be formed from a light transmitting polymer since reading of the wells occurs through use of their light transmitting properties. In order that the antisera and reagents necessary for a diagnostic assay spread evenly into the bottom of the reaction well when the loaded, it is necessary to treat the plastic surface to make it wettable. This is usually done, as disclosed in Akerman, et al., PCT International Application W087/02619, May 7, 1987 by oxidizing the inner surface of the reaction wells by conventional electrode discharge devices such as a corona discharge. Without this treatment the drops of fluid would remain soneroid, as a drop of water on wax paper. In the past, the entire plastic tray is treated or oxidized as it passes under an electrode assembly on a conveyor mechanism. By this process the surface which undergoes the oxidation treatment includes the surface of the bottom of the well, as well as the surface of the side wall of the wells. We have found this to be undesirable since antiserum (reagent) and/or cell (sample) microdrops are not accurately delivered to the center of the well. In fact, these liquid drops fall on a side wall of the well and adhere. In this manner, the liquids for carrying out an immunoassay do not reach the bottom of the well where they should meet and mix with a suitable component (sample or reagent) in order that the immunogenic reaction can take place.
We have found that the poor mixing and adherence to the side walls is troublesome in using this microtiter plates. It is difficult to direct the very small microdrops (1 microliter) exactly to the center of the well at each time, as ideally it should. Everytime a microdrop is inaccurately delivered so that it adheres to a side wall of a well, and this is noticed by the technician who carries out the assay, the technician should properly try to make sure that the cells to be tested get properly mixed with with the antiserum at the bottom of the reaction well. For this purpose he may have to use a stirring wire and/or carry out a centrifuqation of the tray.
Unfortunately, since the microdrops (antiserum or cells) are so small, not every inaccurate delivery thereof to a side wall of the well is noticed and corrected by necessary mixing operation carried out by the technician. Thus when such inaccurate delivery of the microdrops takes place and remains unnoticed, the cells under test and the antiserum are not mixed with each other and a false negative reaction results. It is therefore highly desirable to overcome this difficulty in order to improve the reliability of the assays.